Catalyst for low temperature cure of blocked isocyanates

ABSTRACT

The present invention comprises a curable composition comprising: 
     (i) a blocked reactive component comprising a blocked isocyanate or a blocked isothiocyanate; 
     (ii) a functional compound containing reactive hydrogen; 
     (iii) a triorganotin catalyst for promoting the reaction of the blocked reactive component with the functional compound. 
     The composition may also be admixed with water. The invention also relates to a method for curing a blocked isocyanate or blocked isothiocyanate at a temperature below about 150° C. which comprises combining a triorganotin compound with the blocked reactive component and functional compound and heating at a temperature less than about 150° C. to obtain a cured urethane or thiourethane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to tin catalysts to promote the lowtemperature cure of blocked isocyanates and blocked isothiocyanates.

2. Description of Related Art

Organotin compounds, particularly diorganotins, are commonly used forthe curing reaction of blocked isocyanates with hydroxyl-containingcompounds. These systems find applications in coatings, where thehydroxyl-containing compound is polymeric and the blocked isocyanate ismultifunctional. Frequently, the blocking agent is an aliphatic alcohol,which imparts long pot life in one pot systems. Reaction of the pendanthydroxyl groups with the multifunctional blocked isocyanate occurs atelevated temperatures in a cross-linking reaction which increases themolecular weight and results in a cured coating which has excellentsolvent resistance.

Due to environmental considerations, the coatings industry has beenturning to systems wherein the reactants are dispersed in an aqueoussystem. These systems require the formation of stable dispersions andhydrolytic stability for all reactants. In particular, primer coatingsmay be deposited from aqueous dispersion onto metal surfaces by cathodicdeposition, as described by Bosso et al., U.S. Pat. No. 4,101,486.

Catalysts are usually needed in order to promote the curing reactionwhen the blocking agent is an aliphatic alcohol. Conventionally, thesecatalysts are stannous salts or mono- or diorganotin compounds whichcatalyze the curing or cross-linking reaction at temperatures in therange 330°-365° F. It is often desirable to obtain curing reactions atlower temperatures in order to conserve energy, reduce deformation ofplastic parts attached to the metal object, and reduce color formation.

Thiele et al., Plaste und Kautschuk, 36 January 1989 (1) pp. 1-3,disclose the reaction of phenylisocyanate and butanol in the presence ofbis tributyltin oxide as a model reaction for urethane polymers whereinthe addition of one mol percent water retarded the rate of reaction andcaused a deviation in the linearity in Eyring diagrams. The retardingeffect of the water may be reduced by increasing the temperature. Thereference suggests that triorganotin catalysts are not suitable inaqueous systems where lower temperature cures are required.

Jerabek U.S. Pat. No. 4,031,050, Jerabek et al., U.S. Pat. No. 4,017,438and Bosso et al. describe aqueous coating compositions based on blockedorganic polyisocyanates, an amine adduct of an epoxy group-containingresin and a diorganotin catalyst. These compositions are cationic andmay be electrodeposited on a cathode and are widely employed as primersfor automotive substrates. In this process, a conductive article such asan auto body or an auto part is immersed in a bath of the aqueouscoating and acts as an electrode in the electrodeposition process. Anelectric current is passed between the article and a counter-electrodein electrical contact with the aqueous coating until a desired coatingthickness is deposited on the article.

The amine adduct of the epoxy resin is cationic and is readily coated oncathodic metal substrates such as auto bodies or auto parts. The coatingoperation may be conducted as a continuous process which requires thebath to be monitored and replenished periodically with the coatingcomposition and/or components of the composition which are depleted assuccessive coating operations are carried out.

The diorganotin catalyst employed is a solid that is dispersed in thecoating composition and in some instances will separate from the coatingand deposit, with other coating residues, on the bottom of the tankwhich contains the coating bath. The amount of catalyst in the bath,therefore can be depleted requiring that it be replenished so that thecure of the coating is effected in a timely manner. Replenishing thesolid catalyst can be difficult or a disadvantage since it has to beproperly dispersed in a suitable medium before being introduced into thebath.

Although these cationic amine adducts of the epoxy resin can beformulated with pigments and/or fillers, attempts are being made toprovide coating systems that do not have any solid materials in them asa cost savings measure and also to eliminate various problems in thecoating tank with solid materials settling to the bottom of the tankwhich include solid organotin compounds. These materials that settlehave to be separated by an ultrafiltration process and where catalyst isremoved in this process, it has to be replaced. An essentiallysolids-free coating system would therefore be desirable to avoid orminimize the settling problem. Additionally, the expense of preparingsuch a coating could be reduced by eliminating any grinding step thatwould be required to disperse catalysts and/or pigments, fillers and thelike in the coating composition.

Coatings without pigments or fillers can be used as first coats inseveral applications where subsequent coats would provide the pigmentmaterials that are in some instances necessary to protect the coatingfrom ultraviolet radiation or other environmental hazards that couldcause the coating to deteriorate at an unacceptable rate.

If coatings of this type can be applied electrolytically at a fasterrate as well as cured at a faster rate, an increase in production rateswould be obtained which represent a cost savings to the manufacturer.

Although the cationic amine-epoxy resins can be applied to metallicsubstrates electrolytically, these types of coatings are self-limitingby which it is meant that after a certain thickness, the coating buildup slows and eventually stops since the coating material is insulating.Higher build coatings are an advantage since equivalent coatingthicknesses can be applied more quickly or the full thickness of thecoating can be obtained to provide improved physical properties such asimpact resistance, corrosion resistance and the like.

Additionally, one problem encountered with some prior art coatings ofthis type is the inability to obtain a sufficient coating thickness atthe edge of the object being coated. Edges, with this reduced coatingtend to wear or corrode faster and can be regions on the metal articlewhere a loss of structural integrity will occur first.

It is also desirable to eliminate pigments and/or fillers in coatingcompositions of this type since they are a source of pinholing in thecoating which compromises the integrity of the coating layer andconsequently exposes the metal substrate to wear and corrosion.

It would therefore be an advantage to obtain a catalyst that wouldpromote the cure of these type of coatings at substantially the samerate as the catalyst presently used and which would be easilyincorporated into the coating composition and would not tend to separateduring use. Catalyst that are liquids at coating conditions and whichare either soluble or readily dispersible, i.e., emulsified in thecoating composition would be especially preferred in this regard.

Chung et al. U.S. Pat. No. 5,116,914 notes that dibutyltin oxide, whichis used as a catalyst in these aqueous coatings is difficult to dispersewhereas dibutyltin dilaurate can be hydrolyzed which causes crateringproblems in the deposited film. The patentees describe the use of adibutyltin diacetyl acetonate catalyst to avoid these problems.

Treadwell et al. U.S. Pat. No. 4,032,468 describes the use of atrimethyl or a trimethylmethoxytin oxide catalyst for the preparation ofhydrolytically stable urethane foam precursors. The foam is formed bythe reaction of the isocyanate component of the urethane foam withwater.

Coe U.S. Pat. No. 4,286,073 describes the use of tributyltintoluenesulfonate or methanesulfonate catalysts for the manufacture ofurethanes whereas Groves, U.S. Pat. No. 4,087,412 teaches a mixture oftrialkyltin oxide and a reaction product of a carboxylic acid and adialkyl tin oxide catalyst for the formation of polyurethane polymers.Zemlin, U.S. Pat. No. 3,523,103 describes the use of a tri-organoditincatalyst for the formation of polyurethanes.

Accordingly, catalysts that would not detract from the stability of theelectrolytic bath employed according to the Jerabek, Jerabek et al. andBosso et al. patents would be advantageous. Additionally, it would be anadvantage to provide a catalyst that had improved throwing power in suchbaths, i.e., an increase in the amount of coating deposited in remoteareas. Catalysts that also promote the deposition of coatings from thesebaths at a lower weight but afford equivalent protection as do heaviercoatings are also desirable. When used as automotive coatings, thiswould result in some reduction in automobile weight leading to somemeasure of emission reduction and improvement in fuel economy. Otherproperties which are sought in these types of catalysts include improvedultrafiltration, reduced grind preparation, increased deposition rate,improved dispersability or emulsifiability, reduced cure temperatures,easier handling, improved color maintenance and a lower level ofcatalyst used.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a composition and aprocess that substantially obviates one or more of these and otherproblems due to limitations and disadvantages of the related art.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the composition of matter and process, particularly pointedout in the written description and claims hereof.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described, the inventioncomprises a curable composition comprising:

(i) a blocked reactive component wherein the blocked reactive componentis a blocked isocyanate or a blocked isothiocyanate;

(ii) a functional compound reactive with the blocked reactive component,the functional compound containing reactive hydrogen;

(iii) a triorganotin catalyst for promoting the reaction of the reactivecomponent with the blocked functional compound.

The composition may also be admixed with water.

The invention also relates to a method for curing a blocked isocyanateor blocked isothiocyanate at a temperature below about 150° C. whichcomprises combining a triorganotin compound with the aforesaid blockedreactive component and functional compound and heating at a temperatureless than about 150° C. especially from about 130° to less than about150° C. to obtain a cured urethane or thiourethane.

DETAILED DESCRIPTION

This invention discloses triorganotin-based catalysts which promote thecure of blocked isocyanates and especially aliphatic alcohol-blockedisocyanates or isothiocyanates at temperatures lower than about 150° C.It is unexpected that the triorganotin compounds, which are notconventional catalysts for urethane or thiourethane reactions shouldfunction as catalysts at lower temperatures than conventionaldiorganotin compounds such as dibutyltin oxide. The catalyst of thepresent invention comprises a triorganotin catalyst for promoting thereaction of a blocked isocyanate or isothiocyanate with a compoundhaving active hydrogen and comprises: R₃ SnA wherein each R is ahydrocarbyl group bonded directly to tin through carbon and may be thesame or different, branched or unbranched, saturated or unsaturated,substituted or unsubstituted comprising C₁ to about C₁₈ alkyl, C₆ toabout C₂₀ aryl, cycloalkyl, alkaryl, vinyl and allyl, A is --O--SnR₃,--S--SnR₃, --O--SnR₂ X, --O--SnRX₂, --SR, ##STR1## X, in which R is asdefined above, R' is a divalent hydrocarbyl group which may be saturatedor unsaturated, branched or unbranched, substituted or unsubstituted,aryl C₆ to about C₂₀, alkyne of about C₄ to C₂₀, "p" represents apolymer of 5 to 1000 repeating units, X is an anion comprising chlorine,bromine, iodine, fluorine, hydroxyl, carboxyl, alkoxy, hydride,sulfonate, toluene sulfonate, C₁ -C₅ alkyl sulfonate, phosphate,silicate, carbonate and isocyanate.

These catalysts comprise:

Triorganotin catalysts for the reaction of "blocked" isocyanates withactive hydrogen components and include:

I. bis-(triorganotin)oxides of the formula:

R¹ R² R³ Sn--O--Sn R⁴ R⁵ R⁶ wherein each R is a hydrocarbyl group bondeddirectly to tin through carbon and may be the same or different and is:

alkyl of C₁ to about C₁₈ which may be branched or unbranched, saturatedor unsaturated, substituted or unsubstituted; aryl, alkaryl, cycloalkyl,vinyl or allyl, all of which may be substituted or unsubstituted byhalo, hydroxyl, C₁ to about C₁₀ aryl and C₁ to about C₅ alkyl groups.

Examples of this class of triorganotins include:

bis (trimethyltin) oxide

bis (triethyltin) oxide

bis (tripropyltin) oxide

bis (tributyltin) oxide

bis (triamyltin) oxide

bis (trihexyltin) oxide

bis (triheptyltin) oxide

bis (trioctyltin) oxide

bis (tri-2-ethylhexyltin) oxide

bis (trinonyltin) oxide

bis (tridecyltin) oxide

bis (tridodecyltin) oxide

bis tris(tridecyl)tin! oxide

bis tris(pentadecyl)tin! oxide

bis tris(hexadecyl)tin! oxide

bis tris(heptadecyl)tin! oxide

bis tris(octadecyl)tin! oxide

(trimethyltin) (tributyltin) oxide

(tributyltin) (tri-n-octyltin) oxide

(trioctyltin) (trioctadecyltin) oxide

(dioctylbutyltin) (trioctyltin) oxide

bis (trioleyltin) oxide

bis (3,3,5 trimethylpentyltin) oxide

bis (triphenyltin) oxide

bis (tricyclohexyltin) oxide

bis (tribenzyltin) oxide

bis (trivinyltin) oxide

bis (triallyltin) oxide

(triallyltin) (trioctyltin) oxide

bis (tritolyltin) oxide

bis tri(monohydroxyoctyl)tin! oxide

bis (tri-para-chlorophenyltin) oxide

II. bis (triorganotin)sulfide of the formula:

R¹ R² R³ Sn--S--Sn R⁴ R⁵ R⁶ wherein each R is a hydrocarbyl group bondedto tin and is taken from the same R groups as described in I. above.

Examples of this class include:

bis (trioctyltin) sulfide

bis (tributyltin) sulfide

bis (trilauryltin) sulfide

bis (triphenyltin) sulfide

III. (triorganotin) (diorgano X tin) oxide of the formula:

R¹ R² R³ Sn--O--Sn R⁴ R⁵ X wherein each R group is a hydrocarbyl groupbonded to tin through carbon and is taken from the same R groups asdescribed in I. above. X is carboxyl of 1 to about 20 carbon atoms,halide, hydroxyl, sulfate, mercapto, the residue of a mercapto acid,mercapto alcohol or esters thereof.

Examples of this class include:

(trioctyltin) (dioctylmethoxytin)oxide

(tri-2-ethylhexyltin) (dioctylchlorotin) oxide

(trioctyltin) (dioctyllaurylcarboxytin) oxide

(trioctyltin) (dioctylhydroxytin) oxide

(tributyltin) (dibutyliso-octylmercaptoacetatotin) oxide

IV. (Triorganotin) (diorgano X tin) sulfides and sulfones of theformula:

(R¹ R² R³ Sn) (R⁴, R⁵, X Sn) Sulfides wherein each R group is ahydrocarbyl group bonded to tin through carbon and is taken from thesame R groups as described in I. above. X is carboxyl of C₁ to about C₂₀atoms, halide, hyroxyl, sulfate, mercapto, a residue of a mercapto acid,mercapto alcohol or esters thereof. S is sulfur or sulfone.

Examples of the class include:

(trioctyltin) (dioctyl, chlorotin) sulfide

(trioctyltin) (dioctyl, hydroxytin) sulfone

V. bis (triorganotin) dicarboxylates of the formula:

R¹ R² R³ Sn O₂ C--X--CO₂ --Sn--R⁴, R⁵, R⁶ wherein each R is ahydrocarbyl group bonded to tin through carbon and is taken from thesame R groups as described in I. above. X is an alkyl group of C₁ toabout C₁₈, alkenyl of C₂ to about C₁₈, alkyne of about C₄, cyclohexenyl.

Examples of this class includes:

bis (trioctyltin) adipate

bis (tributyltin) maleate

bis (trioctyltin) cyclohexene dicarboxylate

VI. bis (triorganotin) dimercaptide of the formula:

R¹ R² R³ Sn--S--X--S--Sn R⁴ R⁵ R⁶ wherein each R is a hydrocarbyl groupbonded to tin through carbon and is taken from the same R groups asdescribed in I. above. X is an alkyl group of C₁ to about C₁₈, alkyne ofabout C₄, cyclohexenyl or paraxylyl.

Examples of this class include:

bis (trioctyltin) α.sup.∝ dimercaptoparaxylene

bis (trioctyltin) cyclohexenedimercaptide

(trioctyltin) (dioctyl, lauryltin) dimercapto hexylene

VII. Triorgantoin Salts of the formula:

R¹ R² R³ Sn X wherein each R is a hydrocarbyl group bonded to tinthrough carbon and is taken from the same R groups as in I. above. X ishalo, chloro, bromo, iodo, fluoro, C₁ to about C₅ alkoxy, hydroxy,carbonate, phospate, phosphinate, isocyanate, sulfonate, carboxylsubstituted or unsubstituted of C₁ to about C₂₀ carbon atoms,siloxinate, ethoxylate.

Examples of this class include:

tributyltinfluoride

trioctyltinchloride

trioctyltinoctanoate

trioctyltinmethoxide

trioctyltinhydroxide

trioctyltincarbonate

tributyltinphosphate

trilauryltinphosphate

trioctyltinisocyanate

trioctyltinphenate

trioctyltin-9,10-dihydroxystearate

VIII. (triorganotin) (mono-organtotin) oxides of the formula:

R¹ R² R³ Sn--O--Sn R⁴ X Y wherein each R is a hydrocarbyl group bondedto tin through carbon and is taken from the same R group described in I.above. X and Y may be the same or different and are halo, chloro, bromo,fluoro, hydroxyl, oxy, sulfur, carboxylate of C₁ to about C₂₀, alkoxy, amercapto residue of a mercapto alcohol, mercapto acid or esters thereof.

Examples of the class include:

(trioctyltin) (mono-octyldihydroxytin) oxide

(triphenyltin) (monobutyldichlorotin) oxide

IX. bis (triorgano) ditin of the formula:

R¹ R² R³ Sn--Sn R⁴, R⁵, R⁶ wherein R is a hydrocarbyl group bondeddirectly to tin through carbon and is taken from the same R groups asdefined in I. above.

Examples of the class include:

bis (trioctyl) ditin

bis (tributyl) ditin

X. Polymer bound triorganotin of the formula: ##STR2## wherein each R isa hydrocarbyl group bonded to tin through carbon and is taken from thesame R groups described in I. above. C--C--C--C!_(x) is representativeof a polymer backbone group having a molecular weight of 2000 orgreater, such as: ##STR3## when R is as defined above, R" is hydrogen,methyl or ethyl, a+b represent a polymer of 5 to 1000 repeating units,b÷a is from about 1 to about 20 and especially from about 3 to about 10.

It is to be understood that commercially produced products of the abovedescribed triorganotins may contain small quantities of organotin otherthan the principle component. It is also to be understood that where dior multifunctional anions or cations are present in the triorgantinstructure, oligomerization, cyclization or polymerization may occur.Further, in all triorganotin components except when R¹ R² R³ and R⁴ R⁵R⁶ are the same, equilibrium, mixtures may exist. Mixtures, andespecially two, three or four component mixtures of the foregoing tincatalyst may also be used.

Triorganotin compounds useful as satisfactory catalysts in the reactionof blocked isocyanates with active hydrogen containing materials such aspolyols depend not only on the structure and physical form of thetriorganotin compound, but also on the presence or absence of solvents,processing temperature, and the composition of the reactants.

Tin catalysts that may be especially employed according to the inventioncomprise tributyltin oxide and especially bis(tri-n-butyltin) oxide,bis(trioctyltin) oxide and especially bis(tri-2-ethylhexyltin) oxide,bis(triphenyltin) oxide and triphenyltin hydroxide and othertriorganotin catalysts such as tributyltin fluoride, triallyltinchloride, tributyltin hydride, triphenyltin hydride, tributyltinhydroxide, tributyltin methoxide, tributyltin butoxide, tributyltinacetate, tributyl N-piperazinylthiocarbonylmercaptide,tributyltinphosphorus dibutoxide, and bis-tributyltin oxide. Other tincatalysts that may be employed comprise tributyltin toluenesulfonate andtributyltin methanesulfonate, bis (trimethyltin) oxide, bis(trimethylmethoxytin) oxide and organoditin compounds such ashexabenzylditin, bis-trimethyltin, hexaethylditin, hexa-n-butylditin,hexaphenylditin, hexastearylditin, hexalaurylditin,trilauryltributylditin, hexaoctylditin. Various mixtures of theaforesaid tin catalysts can be used, especially the two or three or fourcomponent mixtures.

This triorgano tin catalyst in which each hydrocarbyl group bonded totin is an alkyl group of C₈ to C₂₁ exhibits low toxicity and coatingcompositions using these catalysts present reduced environmental andhealth hazards.

In general, it is desirable that the triorganotin compound be a liquidat room temperature (about 25° C.) or be soluble in the reactant orconventionally employed solvent compatible with the system. Thus, thechoice of triorganotin catalyst will be strongly influenced by the totalsystem and the result sought.

The tin catalyst of the present invention can also be employed incombination with other known urethane catalysts such as known metalcompounds which are used as catalysts or basic materials such as aminesand alkali metal or alkaline earth metal salts and compounds. Tertiaryamines having relatively high basicity are especially suitable in thisregard. Additionally, azo compounds can be employed such as1,4-diazabicyclo 2.2.2!octane, also known as triethylenediamine as wellas 1-azabicyclo 2.2.2!octane and 1,8-diazabicyclo 5.3.0!undec-7-ene.

Heterocyclic nitrogen compounds can also be employed such as pyridine,pyrazine, pyrimidine, pyridazine, indolizine, phenazine, isoquinoline,quinoline, phthalazine, naphthrydine, quinoxaline, quinazoline,cinnoline and their derivatives.

Other amines and especially tertiary amines that may be employed asco-catalysts such as tri-lower alkyl amines are further described inKirk-Othmer Encyclopedia of Chemical Technology, Third Edition under theheading "Amines" which is incorporated herein by reference.

Bismith and lead compounds may also be employed as co-catalysts asdescribed by Britain et al., J. Appl. Polym. Sci. 4, 207 (1960) which isincorporated herein by reference as well as metal acetylacetonates basedon manganese, vanadium, iron, copper, cobalt and chromium. Carboxylicacid salts of calcium, cobalt, manganese, zinc and zirconium may also beemployed. Organomercury compounds or organolead compounds such as phenyllead triacetate or lead hydrides or lead salts can also be used wheretoxicity is not a consideration. Generally, the heavy metal co-catalystsare not employed because of toxicity problems.

Other co-catalysts that may be employed include lithium oxide; sodiumand potassium alkoxides; sodium formate, carbonate, benzoate, andborohydride; potassium and calcium acetates; alkali soaps; metalnaphthenates; N,N-dimethylformamide; and Friedel Crafts-type catalysts.Additionally, potassium salts of carboxylic acids, ammonium salts ofcarboxylic acids and other tertiary amines, such as2,4,6-tris(N,N-dimethylaminomethyl)phenol,1,3,5-tris(3-dimethylaminopropyl)hexahydro-s-triazone, as well asammonium salts can be used.

The terms "isocyanate" and isothiocyanates are used herein to refer tomono- and polyisocyanates and to mono- and polyisothiocyanates,respectively, including particularly diisocyanates anddiisothiocyanates. While the invention has been described specificallywith reference to the reaction of certain diisocyanates, it is generallyapplicable to the reaction of any compound containing one or more--N═C═Y groups in which Y is oxygen or sulfur. Examples ofpolyisocyanates suitable for the present invention include aliphaticcompounds such as trimethylene, tetramethylene, pentamethylene,hexamethylene, 1,2-proplylene, 1,2-butylene, 2,3-butylene, 1,3-butylene,ethylidine and butylidene diisocyanates. Additionally, the cycloalkylenediisocyanates can be employed such as 1,3-cyclopentane, 1,4-cyclohexane,and 1,2-cyclohexane diisocyanates. The aromatic diisocyanates may alsobe used such as m-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthaleneand 1,4-napthalene diisocyanates as well as the aliphatic-aromaticdiisocyanates such as 4,4'-diphenylene methane, 2,4- or 2,6-tolylene ormixtures thereof, 4,4'-toluidine, and 1,4-xylylene diisocyanates. Thenuclear substituted aromatic diisocyanates may also be employed such asdianisidine diisocyanate, 4,4'-diphenylether diisocyanate andchlorodiphenylene diisocyanate, 1,8-diisocyanato-p-menthane,1-methyl-2,4-diisocyanatocyclohexane, chlorophenylene diisocyanates,diphenyl-methane-4,4'-diisocyanate and naphthalene-1,5-diisocyanate.Additionally, the triisocyanates such as triphenylmethane-4,4',4"-triisocyanate, 1,3,5-triisocyanate benzene and2,4,6-triisocyanate toluene may also be employed. Tetraisocyanates maybe utilized such as 4,4'-diphenyl-dimethylmethane-2,2',5,5'-tetraisocyanate as well as other isocyanates such asxylylene-α,α'-diisothiocyanate, isopropylbenzene-α,4-diisocyanate andpolymerized polyisocyanates such as tolulene diisocyanate dimers andtrimers; dianisidine, diisocyanate (CAS Registry No. 91-93-0); tolidinediisocyanate (CAS Registry No. 91-97-4); biuret of hexamethylenediisocyanate (CAS Registry No. 4035-89-6); isophorone diisocyanate (CASRegistry No. 4098-71-9); polymeric diphenolmethane diisocyanate (CASRegistry No. 9016-87-9) or 4,4'-dicyclohexylmethane diisocyanate.Various mixtures of isocyanate may also be used especially the two,three, or four component mixtures.

The organic polyisocyanates may also be a prepolymer derived from apolyol and a polyisocyanate so that the polyol contains an isocyanategroup or groups where the polyols include polyether polyols or polyesterpolyols or simple polyols such as glycols, including ethylene glycol andpropylene glycol as well as glycerol, trimethylolpropane, hexanetriol,pentaerythritol, and the like.

As noted herein, the isocyanate of the present invention comprises ablocked isocyanate which is to say that the reactive isocyanate groupsare reacted with any suitable aliphatic, cycloaliphatic, aromatic, oralkyl monoalcohol or phenolic compounds such as, for example, loweraliphatic alcohols including methyl, ethyl, chloroethyl, propyl, butyl,amyl, hexyl, heptyl, octyl, nonyl, decyl and lauryl alcohols, and3,3,5-trimethylhexanol and the like. The aromatic-alkyl alcohols includephenylcarbinol and methylphenylcarbinol. Glycol ethers may be employedsuch as ethyl glycol monoethyl ether, ethyl glycol monobutyl ether andequivalents thereof. The phenolic compounds which may be employedcomprise phenol, substituted phenols such as cresol, xylenol,nitrophenol, chlorophenol, ethyl phenol, t-butyl phenol and2,5-di-t-butyl-4-hydroxy toluene. Other blocking agents that may beemployed include tertiary hydroxyl amines such as diethylethanolamine,lactams such as caprolactam and oximes such as methyl ethyl ketoneoxime, acetone oxime and cyclohexanone oxime. Use of the oximes andphenols in some instances is desirable because some specificpolyisocyanates blocked with these oximes or phenols uncap at relativelylow temperatures.

Bis (cyclic ureas) are blocked aliphatic diisocyanates and are preferredin some embodiments because no by-products are formed upon thermalrelease of the reactive isocyanate groups. These comprise compounds thatcan be referred to as self blocked isocyanates. Examples of thesebis-cyclic ureas are described by Ulrich, ACS Symp. Ser. 172 519 (1981),Sherwood, J. Coat. Technol. 54 (689), 61 (1982) and Kirk-OthmerEncyclopedia of Chemical Technology, Third Edition, Volume 23, p. 584all of which are incorporated herein by reference. Blocked isocyanatesof the following formula bis (cyclic ureas)! are especially of interestwhere R is a C₁ to about C₁₀ hydrocarbon radical: ##STR4##

The blocked reactive isocyanate or isothiocyanate of the presentinvention is reacted with a functional compound containing a reactivehydrogen as determined by the Zerewitinoff method described in J. Am.Chem. Soc., Vol. 49, p. 3181 (1927). These compounds containing activehydrogens comprise compounds used for manufacturing a polyisocyanateprepolymer as previously described, e.g., polyols including polyetherpolyols or polyester polyols which is to say compounds containinghydroxyl groups. Additionally, compounds containing amino groups arealso included within those materials that are functional compoundscontaining reactive hydrogen but generally include all compounds whichgive a positive test for reactive hydrogen as determined by theZerewitinoff method. These compounds include but are not limited to,alcohols, hydroperoxides, phenols, boronic acids, carboxylic acids,percarboxylic acids and sulfonic acids and the like. Also includedwithin this group are compounds containing a nitrogen-hydrogen bond suchas amines, amides, lactams, ureas, urethanes, allophanates, biurets,acyl ureas, thioureas, hydrazines, oximes, amidines, hydroxylamines,hydrazones, hydroxamic acids, nitramines, diazoamino compounds andsulfonamides. Compounds containing a sulfur-hydrogen bond are alsoincluded such as mercaptans, thiophenols and thioacids. Other compoundswhich are included are halogen acids, compounds containing activemethylene groups and compounds capable of forming enols such as acetone,malonic esters, acetoacetic esters, acetylacetone and nitromethane andmiscellaneous active hydrogen-containing compounds such as acetyleniccompounds and dialkyl phosphonates. Compounds containing two or more orany one or combination of active hydrogen groups already described arealso included.

The functional compound may also comprise a resin which is an adduct ofa primary and/or secondary amine with an epoxy group-containing resin ora resin which is an adduct of an amine-acid salt with a polyepoxide.

The epoxy material utilized to form the adduct can be any monomeric orpolymeric compound or mixture of compounds having an average of one ormore epoxy groups per molecule. A particularly useful class ofpolyepoxides are the polyglycidyl ethers of polyphenols such asBisphenol A or polyepoxides produced from novolak resins or similarpolyphenol resins. These epoxy resins are especially suitable for thepreparation of amine adducts of epoxy resins which are based on primaryor secondary amines and especially secondary amines and where theadducts are further reacted with an acid to provide catonic groups inthe adduct.

Other polyglycidyl ethers of polyhydric alcohols may be employed, suchas those based on ethylene glycol and the like as well as polyglycidylesters of polycarboxlic acids. Polyepoxides derived from the epoxidationof an olefinically unsaturated alicyclic compound can also be used.Other epoxy-containing compounds and resins that may be employed includenitrogeneous diepoxides such as those disclosed in United States PatentNumber U.S. Pat. No. 3,365,471; U.S. Pat. No. 3,391,097; U.S. Pat. No.3,450,711; U.S. Pat. No. 3,312,664; U.S. Pat. No. 3,503,979 and BritishPatent No. 1,172,916 all of which are incorporated herein by reference.

Another class of polyepoxides which may be employed are acrylic polymersformed by copolymerizing an unsaturated epoxy-containing monomer suchas, for example, glycidyl acrylic acid, glycidyl acrylates ormethacrylates, a hydroxyl-containing unsaturated monomer such as ahydroxyalkyl ester of an acrylic acid or methacrylic acid and at leastone other unsaturated monomer such as styrene, alpha-methylstryene, vinytoluene and the like or olefinic acids and esters of acrylic acid ormethacrylic acid such as, methyl acrylate, ethyl acrylate, methylmethacrylate and the like. These epoxy resins are especially suitablefor the preparation of solubilized polyepoxide adducts having aquaternary ammonium salt group e.g., those having a backbone derivedfrom the interpolymerization of an olefinically unsaturated glycidylcompound, a hydroxy alkyl ester of an acrylic acid or methacrylic acidand at least one other olefinically unsaturated monomer. Polyglycidylethers of a polyphenol may also be employed as epoxy resins in thepreparation of the solubilized polyepoxide adducts having quaternaryammonium salt groups.

Epoxy resins which are an adduct of a primary and/or a secondary aminemay be obtained by reacting such epoxy resins with an amine such as awater soluble amino compound including mono- and dialkylamines such asmethylamine, ethylamine, propylamine, butylamine, dimethylamine,diethylamine, dipropylamine, dibutylamine, methylbutylamine, and thelike. Higher molecular weight monoamines may be employed where it ispreferred that the molecule be more flexible. Further, a mixture of lowmolecular weight and high molecular weight amines may also be employedto modify resin properties.

Quaternary ammonium group-containing epoxy resins are obtained byreacting the polyepoxide with an amine-acid salt, preferably a tertiaryamine-acid salt, to form a quaternary amine salt group-containing resin.Primary and secondary amine-acid salts may be employed but the tertiaryamine-acid salt is preferred.

Examples of amine-acid salts which may be employed include amine saltsof boric acid or an acid having a dissociation constant greater thanthat of boric acid and preferably an organic acid having a dissociationconstant greater than about 1×10⁻⁵ such as lactic acid, acetic acid,formic acid, propionic acid, butyric acid, hydrochloric acid, phosphoricacid, sulfuric acid and the like. The amine-acid salt and thepolyepoxide are reacted in the presence of water and the adduct thusobtained.

An amine adduct of an epoxy group-containing resin that is employedaccording to the invention is further described by Jerabek, U.S. Pat.No. 4,031,050, Jerabek et al., U.S. Pat. No. 4,017,438 and the resincontaining active hydrogen atoms and quaternary ammonium groups preparedby the reaction of a polyepoxide with an amine salt that is employedaccording to the invention is described by Bosso et al., U.S. Pat. No.4,101,486, all of which are incorporated herein by reference.

The functional compound reactive with the blocked isocyanate asdescribed by Jerabek et al. is a polyfunctional compound based on aketimine blocked amine having at least one active amine hydrogen whereinthe ketimine blocked amine is reacted with an epoxy compound. In oneembodiment these compounds are obtained by reacting the diketimine ofdiethylene triamine and methyl isobutyl ketone with a polyepoxide.

The various specific isocyanate and thioisocyanate materials that areemployed according to the present invention as well as functionalcompounds containing reactive hydrogen are further described byHostettler et al. U.S. Pat. Nos. 3,084,177; 3,240,730; 3,392,128 and3,392,153 as well as Jerabek, Jerabek et al. and Bosso et al., all ofwhich are incorporated herein by reference.

The following examples are illustrative of the invention.

A common method for comparing the degree of cure of a coating is todetermine the extent to which a coating is removed by a solvent rub testdescribed in ASTM D 4752-87. This procedure is used in the followingexamples but uses methyl isobutyl ketone in place of methyl ethylketone. Cured panels are tested by rubbing the surface of the panel witha cloth, saturated with methyl isobutyl ketone, for 50 double rubs. Therating system is as follows:

    ______________________________________                                        Rating         Appearance of Coating                                          ______________________________________                                        1              No noticeable effect on coating                                2              Faint abrasion of coating                                      3              Moderate abrasion of coating                                   4              Significant abrasion of coating                                5              Metal surface exposed.                                         ______________________________________                                    

EXAMPLE 1

36.8 g bis(tributyltin) oxide (TBTO) are dispersed with 60.8 g aqueousunpigmented resin solution HEQ-8716 obtained from PPG Industries, Inc.,an epoxy based resin. 10.75 g of the resulting emulsion are added to1824 g of unpigmented E 5993, Trade Name "ED4 Resin" obtained from PPGIndustries, Inc., an aqueous coating composition having a film-formingepoxy based resin to form a mixture. The mixture comprises an electrodepositable cationic composition based on the reaction of an epoxyresin, an amine and a blocked polyisocyanate and does not contain anypigments or fillers. Steel panels, 100×150 cm, are coated on both sideswhen immersed to a depth of 120 cm in the resulting bath byelectrodeposition at 240 volts with initial conductivity of 1 amp for 2minutes. The coated panels are cured for 20 minutes at temperatures from135° to 185° C. and tested for degree of cure by the MIBK rub test. Theresults of this experiment are shown in Table 1.

EXAMPLE 2

57.7 g bis(trioctyltin)oxide (TOTO) are dispersed with 60.8 g aqueousresin solution as in Example 1. 12.91 g of the resulting emulsion areadded to 1824 g of an aqueous composition as in Example 1 and treated asin Example 1. The results of the experiment are shown in Table 1.

EXAMPLE 3

24.0 g bis(triphenyltin)oxide (TPTO) are ground with 32.1 g aqueousresin solution as in Example 1. 11.43 g of the resulting dispersion areadded to 1824 g of an aqueous composition as in Example 1 and treated asin Example 1. The results of the experiment are shown in Table 1.

EXAMPLE 4 Control

308 g dibutyltin oxide (DBTO) are ground with 608 g aqueous resinsolution as in Example 1. 10.0 g of the resulting dispersion are addedto 1824 g of an aqueous composition as in Example 1 and treated as inExample 1. The results of the experiment are shown in Table 1.Dibutyltin oxide is an example of catalysts commercially used for cureof blocked isocyanates.

                  TABLE 1                                                         ______________________________________                                        Ratings for Abrasion by MIBK Rub Test                                         All catalysts 0.53 weight % tin based on sol-                                 ids; Oven cure 20 minutes                                                            Oven Temperature, °C.                                           Catalyst 165.5-185      148.8  135                                            ______________________________________                                        DBTO     1              4      5                                              TBTO     1              1      4                                              TOTO     1              1      3                                              TPTO     1              1      2                                              ______________________________________                                    

These results indicate significantly improved cure by the triorganotinoxides at 300°, compared to the control, dibutyltin oxide.

The voltage for each of the coating procedures in Examples 1-4 was 240volts, while the conductivity dropped from the initial one amp toapproximately zero during the course of the electrodeposition. Theamperage drop for the electrodeposition of coating material employingTOTO in Example 2 was at a slower rate than the rate of drop for theelectrodepositions in Examples 1 and 3-4, resulting in higher filmthickness, especially as compared to the control Example 4 in which DBTOcatalyst was employed.

EXAMPLE 5

Example 1 was repeated however, employing an equivalent amount ofdibutyl tin oxide (DBTO) as a control and was cured at 180° C. and 150°C. The experiment was repeated using 50% and 25% of the tin catalyst ona stoichemetric basis. The panels obtained were subjected to a MIBK rubtest and a solvent extraction test which was conducted by initiallyweighing the 10×5 cm steel panel, coating the panel with a 7×5 cmcoating and curing the panel as set forth in Example 1 followed byweighing the cured coating. The panel was refluxed in acetone for sixhours, weighed and the percent weight loss determined.

The experiment was repeated using various organo tin catalysts in anamount comprising 1.0%, 0.5% and 0.25% tin by weight based on the weightof the resin solids of the coating composition. Panels wereelectrolytically coated at either 240 volts or 220 volts and cured at180° C. and 150° C. and subjected to a MIBK rub test and solventextraction test. The results are reported in Table 2.

The data of Table 2 illustrate that the catalysts of the presentinvention can effect cures of urethane compositions at temperaturesbelow 180° C. and are superior to DBTO at lower temperatures.

                  TABLE 3                                                         ______________________________________                                        % Weight Loss                                                                 Acetone                                                                               180° Cure                                                                           150° Cure                                         Catalyst  % Tin on Solids                                                     Compound (volts)                                                                        1%     0.5%    0.25% 1%    0.5%  0.25%                              ______________________________________                                        DBTO      0.3    -1.5    -0.9  20.6  56.1  72.0                               TOTO      4.5    1.3     0.5   8.1   7.0   20.6                               TOTO      4.8                  8.0                                            TOTO (220)                                                                              3.0    1.9     2.8   5.3   6.4   18.3                               TEHTO     4.6    0.9     0.3   10.7  26.5  47.9                               TBTO      -1.0   0.3     5.2   8.2   26.0  50.3                               TPTH      -0.0   -1.8    4.1   9.5   30.3  53.5                               TDTO (220)                                                                              5.4    1.0     -0.3  7.2   15.5  39.6                               TCTH      5.4    2.1     5.1   17.6  41.2  63.8                               TOTA (240)                                                                              2.7    1.1     3.0   20.3  32.1  56.3                               TOTA (220)                                                                              4.8    5.2     3.3   17.0  24.0  11.4                               TOTL      -2.7   0.1     14.3  42.1  58.6  68.4                               TOTS (220)                                                                              3.0    8.3     20.8  55.6  47.5  62.8                               ______________________________________                                        MIBK                                                                          Double Rubs                                                                           180° Cure                                                                           150° Cure                                                 % Tin on Solids                                                                 1%     0.5%    0.25% 1%    0.5%  0.25%                              ______________________________________                                        DBTO      200+   200+    200+  30    5     2                                  TOTO      200+   200+    200+  200+  40    20                                 TOTO      200+                 200+                                           TOTO (220)                                                                    TEHTO     200+   200+    200+  200+  50    1                                  TBTO      200+   200+    200+  200+  20                                       TPTH      5                                                                   TDTO (220)                                                                              50     200     200+  200+  150   1                                  TCTH      200+   200+    200+  100   5     1                                  TOTA (240)                                                                    TOTA (220)                                                                              200+   200+    200+  50    2     4                                  TOTL      200+   200+    20    2     2     2                                  TOTS (220)                                                                              200+   50      2     3     2     2                                  ______________________________________                                    

The following compounds are employed and listed in Table 2.

Compounds

DBTO (control): Dibutyltin oxide

TOTO: Bis(trioctyltin) oxide

TEHTO: Bis tri(2-ethylhexyl) tin! oxide

TBTO: Bis(tributyltin) oxide

TPTH: Triphenyltin hydroxide

TDTO: Bis(tridodecyltin) oxide

TCTH: Tricyclohexyltin oxide

TOTA: Trioctyltin acetate

TOTL: Trioctyltin laurate

TOTS: Trioctyltin laurylmercaptide

The compositions of the present invention can be employed in themanufacture of surface coating compositions which include pigments andfillers, both of which are well known in the surface coating art.

The coatings are applied to metal substrates electrolytically byimmersing the substrate in a bath of the coating composition andapplying an electric current between the substrate and acounter-electrode in electrical contact with the aqueous coating until adesired coating thickness is deposited on the substrate. The substrateis preferably a cathode.

The metal substrates and especially automobile parts may be coated in anassembly-line manner by arranging the parts on a continuous conveyorbelt and running them through the coating bath continuously whilepassing an electric current between the metal article and a counterelectrode as described previously. When the coating is built to adesired thickness, the substrate will be lead out of the bath, washedand cured at an elevated temperature continuously in an oven until thedesired degree of cure is obtained, whereupon the metal substrate willbe led out of the oven and removed from the coating line for furthertreatment.

During the electrolytic coating, the coating bath through which themetal substrates are passed and coated is continuously or periodicallyreplenished with the coating composition or components of the coatingcomposition such as the resin, and/or tin catalysts as described herein.

The foregoing coating compositions are formulated without any pigment orfiller and the triorgano tin catalysts employed are liquid catalysts orcatalysts that are soluble in the solvent system employed in the coatingcomposition. The liquid organo tin catalysts, are preferably employed.Where the liquid catalysts are employed, the coating composition doesnot require any grinding and shows improved quality in that no "dirt" orprecipitated solids develop in the coating bath due to the coatingcomposition. As a result, no solids or less "dirt" is coated onto themetal substrates and further pumping and filtration of the coatingcomposition in the immersion tank is either eliminated or minimized. Theliquid catalysts that are used in this regard comprise TBTO and TOTO andsatisfactory cures are obtained at about 150° C. (approximately 300° F).Faster coating times i.e., greater throwing power is also obtained usingTOTO as well as thicker coatings. This affords additional impact or chipresistance in applications such as applying the coating to automotiveundercarriages and side panels exposed to impact from road debris. Thesethicker coatings also exhibit better corrosion resistance not onlybecause of their thickness but also because pigments are eliminatedthereby minimizing the amount of pinholing in the coating. Additionally,when employing catalysts such as TOTO better edge coating of the metalparts is also obtained.

The coating compositions using TOTO are also less toxic than othertriorgano tin catalysts employed and present less of an environmentaland health hazard than such other triorgano tin catalysts which is ofsome consequence where the contents of the immersion coating tanks haveto be periodically discharged and replenished.

The coating compositions of the present invention are also applied topolymeric substrates including both thermoplastic and thermosettingpolymers, especially polyolefins, phenolics, polyvinylchlorides,polyvinylidine chlorides and fluorides, polyesters, ABS polymers,acrylics, epoxys, polyamides, Teflon® and the like.

The coating composition is applied by dipping, brushing, spraying,roller coating or by electrodeposition on electroconductive polymericcompositions or metallic substrates.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the curable compositioncontaining a catalyst for the low temperature cure of blockedisocyanates or blocked isothiocyanates as well as the method of theinvention for obtaining such low temperature cures without departingfrom the spirit or scope of the invention. It is intended that thesemodifications and variations of this invention are to be included aspart of the invention, provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A process for increasing the environmental safetyof a coating electrolytically applied to a conductive substrate andcatalyzed with a tin catalyst comprising applying to said substrate acurable conductive coating composition comprising:(i) a blocked reactivecomponent wherein said blocked reactive component is a blockedisocyanate or a blocked isothiocyanate; (ii) a functional compoundreactive with said blocked reactive component, said functional compoundcontaining active hydrogen; (iii) a catalyst consisting essentially of atrialkyl tin catalyst in which said alkyl group has from 8 to 21carbons; (iv) water;passing an electric current between the substrateand a counter-electrode in electrical contact with said coating until adesired coating thickness is deposited on said substrate and curing saidcoating at a temperature below about 150° C.
 2. The process of claim 1wherein said alkyl group has 8 carbons.
 3. The process of one of claims1-2 wherein:(I) said blocked reactive component comprises a blockedpolyisocyanate; and (ii) said functional compound reactive with saidblocked reactive component comprises a polyfunctional compoundcontaining active hydrogens.
 4. The process of claim 3 wherein saidfunctional compound reactive with said blocked polyisocyanate comprisesa polyfunctional compound containing active hydrogens wherein saidactive hydrogens comprise at least hydroxyl hydrogens of a primary amineepoxy adduct or a secondary amine epoxy adduct.
 5. The process of claim3 wherein said functional compound reactive with said blockedpolyisocyanate comprises a polyfunctional compound containing activehydrogens wherein said active hydrogens comprise at least hydroxylhydrogens of a secondary amine epoxy adduct.
 6. The process of claim 3wherein said functional compound reactive with said blockedpolyisocyanate comprises a polyfunctional compound based on a ketimineblocked amine having at least one active amine hydrogen wherein saidketimine blocked amine is reacted with an epoxy compound.
 7. The processof claim 3 wherein said functional compound reactive with said blockedpolyisocyanate comprises a polyfunctional compound containing activehydrogens based on a quaternary ammonium salt group solubilizedsynthetic organic resin formed from reacting a tertiary amine-acid saltwith a polyepoxide which contains glycidyl groups.
 8. A process as inclaim 3 wherein said functional compound reactive with said blockedpolyisocyanate is solubilized with acid to provide cationic groups insaid adduct.
 9. A process as in one of claims 1-2 wherein said catalystis a liquid at about room temperature.
 10. A process as in claim 9wherein said conductive coating composition is substantially free ofsolid pigments or fillers.
 11. The process of claim 3 wherein saidcoating is conducted in a bath and said bath is replenished after thecoating operation is carried out with a replenishing material whereinsaid replenishing material is said coating composition or said catalyst.12. A product produced by the process of claim
 1. 13. A product producedby the process of claim
 2. 14. A product produced by the process ofclaim
 3. 15. A product produced by the process of claim
 4. 16. A productproduced by the process of claim
 5. 17. A product produced by theprocess of claim
 6. 18. A product produced by the process of claim 7.19. A product produced by the process of claim
 8. 20. A product producedby the process of claim
 9. 21. A product produced by the process ofclaim 10.